I dont bother repairing them.....most Is surface mount and quite hard to deal with...tiny components..
I return them......or trash them
The one In my Mame Cab has just failed, for no reason.
Btw......just because they tell you they only have a 12 month warranty, Is not quite true...
Most, actually have a 2 year Manufacturers warranty, so If Its under 2 years old, and you contact the manufacturer direct, and have a whinge, about their crap products, you may be able to get a replacement..
I have actually done this successfully, on a couple of occasions...